The present invention relates to submersible pumps, and more particularly to a controller for submersible pumps that can distinguish between fluids such as oil, air and water. By differentiating between different fluids, the pump can be controlled to only pump certain fluids (such as water), and not others (such as oil). Alarms can be generated for fluids that are not to be pumped. False alarms are prevented by distinguishing, for example, between oil and air.
Various industrial applications require submersible pumps. For example, electric utilities commonly use water submersible pumps in transformer vaults for dewatering the vaults. If water accumulates in a transformer vault, it may short a power line causing substantial problems delivering electricity to a consumer. Accordingly, water submersible pumps are commonly placed in the transformer vault to pump out accumulated rainwater and the like which may seep into the vault.
Electrical transformers are normally filled with an oily fluid for lubricating and cooling the various components of the transformer. This oily fluid has a tendency to leak from the transformer housing into the vault. There is a danger to the environment if the oily fluid is pumped with the water into a waste disposal tank or sewer, as such oily fluids usually contain compounds which are harmful to the environment. Further, if the oil admixes with the water and both are pumped to a treatment disposal facility, suitable separation equipment must be provided to separate the oil from the water so that water can readily be disposed of and the oil recycled, or at least stored in a toxic safe facility. Such separation equipment is an item of considerable expense to a utility.
Hydraulic elevators are another application with similar concerns. In particular, the hydraulic oil in the hydraulic shaft tends to leak into the underground vault which houses the elevator piston. This vault may also fill with water during heavy rains due to underground seepage. It is necessary to pump the water out of the vault without pumping the hydraulic oil.
U.S. Pat. Nos. 4,715,785 and 4,752,188 disclose oil detection apparatus for use in controlling submersible pumps. In the systems described in these patents, a probe is mounted on a water submersible pump. The probe extends into any water that accumulates in the bottom of a transformer vault, enabling a conductive path to be established that is used to activate the pump. As the water level falls during pumping, oily fluids, which are immiscible in the water and rise to a level above the water, will come into contact with the probe. Since the oil is not electrically conductive, it breaks the conductive path, thereby stopping the pump.
It is desirable to generate an alarm in the event that a harmful fluid, such as oil, is detected in an underground vault or the like. Such an alarm can be used to identify a potential problem to a central facility, which can dispatch a technician to investigate further. However, false alarms should be prevented. Such false alarms can occur, for example, if the detection of oil relies on the electrical non-conductivity of the oil, since air (which is also non-conductive) may also set of the alarm.
It would be advantageous to provide a method and apparatus to insure that only water is pumped from an industrial vault, without pumping potentially harmful substances such as oil. It would be further advantageous to provide such a method and apparatus in which oil and air are differentiated in order to prevent the occurrence of false alarms.
The present invention provides the aforementioned and other advantages.